Multiwavelength Surface Plasmon Resonance Sensor Designs for Chemical and Biochemical Detection

Abstract

Surface plasmon resonance (SPR) sensors using multiwavelength light coupling are investigated to probe changes in refractive index that occur as a result of chemical or biochemical processes. Traditional SPR sensors have used angle modulation to facilitate detection at the sensor surface; however, the multiwavelength approach is novel and brings new functionality to SPR sensors. The multiwavelength sensors are constructed on both fiber optic and bulk waveguides such as prisms. A thin metal film is deposited on the waveguide surface to support the surface plasmon (SP) mode. The evanescent field produced by light propagating through the waveguide can be coupled into the surface plasmon mode thus attenuating the transmitted light. This coupling is dependent upon phase matching between the light wavevector and the surface plasmon wavevector. The wavevectors are directly related to the wavelength of light, thickness of analyte on the sensor surface and the refractive index of the analyte. As these parameters change, the light output from the sensor will be affected. Other thin films can be subsequently deposited on the metal to functionalize the sensor surface for a particular analyte of interest. A theoretical background and details of the sensor construction is given. The developed sensors are tested in a variety of application systems. Experimental results for refractive index sensing in bulk liquid applications is shown. Observed sensitivity approaches that of conventional SPR techniques. Alkyl-thiol monolayer systems are studied to investigate kinetics of formation and the thickness resolution of the sensor. A biochemical system is investigated to compare the sensors with other immunoassay techniques. Ionic self-assembled monolayer (ISAM) systems are investigated to probe structure and determine their usefulness as an immobilization layer for biochemical species. A mathematical model based on Fresnel reflection equations is developed to predict sensor response. This model can be used to selectively vary sensor parameters to optimize the response for a specific analyte system or to calculate system parameters based on experimental results. Results from the various experiments are compared with the model. Experimental results and interpretations are discussed along with future work and potential improvements. Classical SPR sensors are also discussed along with comparisons with the multiwavelength sensors. Future improvements to SPR sensors design are considered, as is the application of the technology to high-throughput drug screening for pharmaceuticals.